Polyamide substrates, such as nylon carpeting, upholstery fabric and the like, are subject to staining by a variety of agents, e.g., foods and beverages. An especially troublesome staining agent is FD&C Red Dye No. 40, commonly found in soft drink preparations. Different types of treatments have been proposed to deal with staining problems. One approach is to apply a composition containing a sulfonated phenol-formaldehyde condensation product to the substrate. However, sulfonated phenolformaldehyde condensation products are themselves subject to discoloration; commonly they turn yellow. Yellowing problems are described by W. H. Hemrepel in a Mar. 19, 1932 article in America's Textiles, entitled "Reversible Yellowing Not Finisher's Fault". Hemmpel attributes yellowing to exposure of a phenol-based finish to nitrogen oxides and/or ultraviolet radiation. To deal with the yellowing problem, the condensation products were modified by Liss et al. in U.S. Pat. No. 4,963,409 by acylation or etherification of some of the phenolic hydroxyls. My U.S. application Ser. No. 08/126,149 discloses and claims polyamide fibrous substrates treated with water-soluble or water-dispersible maleic anhydride/alpha-olefin polymers to make them stain-resistant and methods for preparing them. Stain-resistant polyamide substrates treated with the compositions of this invention are disclosed and claimed in my copending application Ser. No. 08/220,896.